Frequently Asked Questions

There are no stupid questions.

Please Contact Us with any of your questions, concerns or confusions.
 We are happy to offer our advice and opinions. 

We are not liable for any damage, loss of funds or harm caused from following any of the information on this page. 
Use our advice and opinions at your own risk.

Recent FAQ

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How do you prevent cold air from entering the house through the inlet and outlet during frigid nights in the winter?

posted Feb 2, 2015, 8:06 AM by Greenhill EnviroTechnologies Inc.

With solar air heating systems, air can be cooled inside the collector when the external temperature is very low and the sun is not shining. If there is an open pathway, some of this cold air might flow into the attached property.

The upper vent is usually unaffected by this issue and normally remains at room temperature. However, the effects of gravity can push the more-dense, cooled air downwards inside the collector. If allowed to flow freely, this air can cool the lower vent and possibly cause a small cool draft to be emitted from the lower vent. In theory, this cooling effect would be no different than the equivalent from a very small glass window, as a collector should be well-insulated, sealed and ideally glazed with insulated material such as twin wall polycarbonate.

To restrict the flow of any drafts, people usually either just cover the outlet at night time, or install a flap over the outlet. Here is a photograph of an example of a flap, you could consider implementing something like this to solve the above problem (if present):

How do I "turn off" my Solar Heaters in the Summer?

posted Dec 11, 2014, 5:54 AM by Greenhill EnviroTechnologies Inc.

A 'stagnant' solar heater in the summer can get very hot, indeed! Too hot in some cases, which can cause damage to the heater, or adjacent elements.

In the summer, if you do not wish to redirect the heat for other uses (such as preheating water for your home or other creative uses, like food/herb drying, clothes drying or heating a hotub/pool...) you can disconnect the Okapi System (or whatever fan control system you have) from its power supply and then decide on your desired way of shading/covering your solar heaters and shielding them from the sun. 

Shading you heater can be done in a number of ways:

1. Attaching a tarp or a rigid, secured covering of some sort.

2. Install an angled sunshade

3. Put up hanging plants, vines on a movable trellis, or a vertical garden that will shade it with their foliage! 


-There are many clever and creative ways of keeping your heaters cool in the summer if you do not plan to use them! 

(If you think of another one, please let us know!)

When connecting Okapi to a PV Panel and Battery system, what kind of battery should I get?

posted Aug 8, 2014, 7:01 AM by Greenhill EnviroTechnologies Inc.   [ updated Aug 8, 2014, 7:08 AM ]


Please review some of these informative sites:

  1. http://www.simplesolarsetup.com/battery4.html -This site has many sections which are great at explaining almost everything.
  2. http://www.solar-electric.com/deep-cycle-battery-types-comparisons.html -Here is another site that gives a general explanation about Deep Cycle Batteries.
  3. http://www.freesunpower.com/batteries.php -Here is another very informative site. It also has other sections (see left navigation bar) about many topics, such as panels and charge-controllers.

It is true, the application of your PV panel and battery system, determines the overall expense. If you only want to run an Okapi System off the battery (and no other appliances), we suggest you look at 40Ah and above for your 12V battery. Batteries with less than 40Ah may not get you though a full semi-cloudy week where the Okapi fans may be running partially, giving you some heat-harvest, but the solar panel may not be charging the battery at all.


Here are the power draws to consider (The values are rounded-up from the actual draws to ensure you do not choose a battery insufficient for your needs):

    1. When Okapi is not running any fans, but is on standby, remaining aware until the next significantly warm collector conditions occur: up to 1W*
    2. When Okapi is running 1 fan at max. speed: 10W*
    3. When Okapi is running 2 fans at max. speed: 20W*
* These values are rounded up  from the actual measured draws to ensure you get a good battery, charge controller and panel system to run Okapi optimally.

These values should allow you to do the necessary simple calculations to choose a 12V "Deep Cycle Battery" that will last for many years, require little to no maintainence and always be able to do the job for you.


Please consult an PV panel and battery system expert and explain your requirements. They can best advise you on your purchase choices. Also, please do not install any battery, charge controller and PV panel yourself without consulting an expert. There are very specific requirements for an PV panel and battery set-up for serious safety reasons. You can put your own life and others at risk, if the set-up is done incorrectly.


Good luck getting your PV panel and battery system set up. Once you do, it will feel great to know you are free from the grid!
Do keep in mind that the Okapi fan control systems have a very low running cost, and will barely effect your power bill, if you do choose to simply plug it into the mains power supply.

Please see the following FAQ link to learn more about the basic PV panel size we suggest: 

Can I use a PV Panel to operate my Okapi 2.i System? How many watts should it be?

WHY are you moving the air from the Ceiling to the Floor? It seems backwards!

posted Aug 6, 2014, 6:35 AM by Greenhill EnviroTechnologies Inc.   [ updated Aug 6, 2014, 7:03 AM ]

Moving warm air from the Ceiling to the Floor! Okapi fan control systems for solar air heaters. Greenhill EnviroTechnologies Inc.

This question is asked the most, in many different ways. Yes, it is backwards and upside down compared to the majority of other Solar Air Heaters out there. That is why Okapi is a true innovation!

Please google/search these words: "moving warm air from ceiling to floor" and you will see there are numerous products for sale, blog-writings, articles and commentary from DIY enthusiasts who are cleverly reducing their heating bills simply by installing products such as a "Heatstick", "Blubox Thermal Fan" or other variations of these concepts.

When any home is heated traditionally, we almost always strive to heat from the bottom up: think installing your furnace or woodstove in your basement or bottom floor, "baseboard heaters", "in-floor heating", HVAC systems that pump warm air out from floor vents... The reason for this traditional approach to heating is because it is the most effective way to heat any space from the bottom up! Then, if you use something like a "Heatstick" or "Blubox Thermal Fan", which is simply a pipe with a fan that draws the warm air that pools at your ceiling (due to convection) down and pumps it back out at the floor level, you can reuse, conserve and store much more of the heat being produced to warm your building. This is technology and science in action: it works!

So, when we designed our Okapi Systems, we automatically thought, just like any other heating system, the solar-heat must come out near floor level to really be effective. And, also, we thought when designing Okapi, it would be doubly effective to draw the air down from the ceiling, through the heater and pump it back out at floor level, because just doing that alone, without additionally solar-heating the air, reduces heating bills already!


-"Very clever upside-down-the-box thinking", was how one of our customers put it!


Can I simply connect the Okapi System directly up to a PV (Photovoltaic) Panel?

posted Jul 30, 2014, 6:53 PM by Greenhill EnviroTechnologies Inc.   [ updated Jul 30, 2014, 6:55 PM ]

We highly discourage and never recommend just connecting an Okapi System directly to a PV Panel (without using a 12V battery and charge controller...) for the following reasons:

1. There could be times when there is not enough power to run the Okapi System optimally or properly, resulting in loss of your heat-harvest. Any solar heat-harvest loss means you will be running your main heating system (furnace, stove, baseboards...) more, costing you more money over time.

2. There could be times when there is too much power produced from the PV Panel, potentially resulting in damage and financial loss.
  • One possible result from this could be the Okapi System shutting down: it is safely fused, so if it does get a power surge the fuse will blow and the system will turn off, (meaning, you would need to buy and insert a new fuse to get it running again).
  • The other possible result is overheating of and damage to the PV Panel itself. The Okapi System will only draw so much power, and if the PV Panel is producing too much, that excess recirculating electricity could potentially cause overheating and possible irreparable damage to your PV Panel, (meaning you might need to buy a whole new PV Panel).

Can I use a PV Panel to operate my Okapi 2.i System? How many watts should it be?

posted Jul 30, 2014, 9:46 AM by Greenhill EnviroTechnologies Inc.   [ updated Jul 30, 2014, 7:32 PM ]

Our Okapi systems can have a free running cost, (which is minimal to begin with) if connected to a 12V battery (it must be a 12V battery) that is charged by a minimum 30 watt PV Panel.

Okapi systems are autonomous, which means they are always on, monitoring the multiple sensors' data about the temperature conditions, in the background, ready to start up the fans automatically, as soon they sense the solar collectors producing sufficient heat.

This means that there is always a mild background power-draw of much less than one watt. For this reason, it is important to have the system safely connected to a 12V battery that is being charged by a minimum 30 watt PV panel. This sized panel should be sufficient to keep both fans running, even at max. speed on sunny days.

However, there is a situation where your Okapi System may not start running immediately on a full-sun day after a week of semi-cloudy days where your fans may have been running at partial speed, harvesting some heat. During this partial cloudy week, there may not have been enough sun to activate the PV Panels to generate enough electricity to charge the battery, and the battery may have run down over this time under this ongoing weather situation.

For this reason, we recommend a 40 watt PV Panel, properly connected to a 12V battery to operate your Okapi 2.i System. Consult the experts at your battery and PV panel retail store to fully understand all the equipment required to safely and properly set up and connect your system.


Please note: You must consult an expert or electrician and follow your local electric code, before installing any PV Panel and battery system. Without a charge controller, proper connections, adequate space and safe, fire-proof materials surrounding your battery and PV Panel connections, you can create a dangerous fire hazard or even an explosion.

Any installation of a PV Panel and battery system for powering an Okapi System is done so at your own risk.

​All that said, once properly set-up, you are ready to go! Enjoy letting Okapi turn the fans on and off and vary their speed accordingly, all by itself, with the peace of mind that you are harvesting as much solar heat as your solar collector can provide and pumping it into your home, garage, shop, cottage or cabin where you can use it most: at floor level.
 -All with a Zero Running Cost.

Isn't it going against the "natural force of convection" to blow the heat down and out near the floor-level?

posted Jul 26, 2014, 8:23 AM by Greenhill EnviroTechnologies Inc.   [ updated Jul 26, 2014, 8:26 AM ]

Natural convection isn't a strong force. 

Picture a campfire on a still night. You can stand next to it and most of the heat is going straight up. Then a gust of wind comes along, and immediately you feel the heat blowing towards you and you have to step back to not get burnt. It doesn't take much to move heat around.

As the air is already flowing through the solar collector downwards, there is essentially no "force of convection" to fight against.

If you want to convince yourself:
  • Put a fan running at full speed at the outlet (near the floor, with the inlet near the ceiling) on a rainy day, when the solar collector would not have any significant heat within it. Measure the actual CFM coming out.
  • Then, on a very sunny day, with a hot solar collector, put the same fan running at full speed at the outlet (near the floor, with the inlet near the ceiling). Measure the actual CFM coming out. 
You should find that there is no significant difference in the CFM in both cases because the "force of natural convection" is very weak.

You might also find that you get more CFM on that sunny day with a hot collector due to the affect of gravity pulling the cooler, more dense inlet air (from the near the ceiling) down through the collector (before it gets heated within the collector).


Isn't it bad for the Fan with the hot air blowing through it?

posted Jul 26, 2014, 7:50 AM by Greenhill EnviroTechnologies Inc.   [ updated Nov 10, 2014, 6:19 AM ]

We have picked our variable speed standard fan especially for its resistance to high heat. It is designed to be able to operate in high-heat temperatures, up to 60C (140F). That is very hot! 

The life of the fans is very long: 70000hrs of continuous use: that works out to almost 8 years running non-stop!!

 If your outlet temperature is much hotter than this, you might have air-flow impedance in your solar collector making the fan labor, and thus not move the air through quickly enough. Either that, or your solar air heater is Huge, and then you should refer to the FAQ about using multiple fans, inlets and outlets for your giant solar air heater. 

The system works best when the fan acts to pull hot air out of the solar collector (through the outlet into the room near floor level). The CFM will always be greater for any fan when it works to pull air out rather than push air in to the solar collector. This is just physics at work.

Many find that in order to get good CFM at their outlet, and they want to blow air into their system at the inlet, they need a really powerful, loud, high CFM fan. However, with that same system, using a less powerful fan pulling the air out of the outlet, you can get better CFM, more air flow.

Why are you pushing the heat out at floor level? No one else seems to be doing this.

posted Jul 26, 2014, 7:22 AM by Greenhill EnviroTechnologies Inc.   [ updated Jul 26, 2014, 7:33 AM ]

One of the greatest innovations of the Okapi Systems is their ability to push the heat out at floor level, because that is the best and most efficient way to heat a room. The heat needs to be stored in the thermal mass of the room (floors, furniture, cushions, pillows, fittings) in order to really keep the room warm. When the heat is blown out at ceiling level, it tends to pool at the ceiling and then conduct outwards through the walls to the outside where it is basically lost and wasted. 

Traditionally, solar air heaters always had the heat coming out at ceiling level because they were passive designs using only the action of natural convection to get the heat into the room. Then people started adding fan systems. Except, to get a fan system to turn on automatically and stay on with a simple snap-disc switch system or thermostat control, it is usually hard to set it all up and get it to blow air out at floor level without the single temperature sensor thinking the collector has cooled down.

With a lot of research and specialized programming of a micro-controller chip, the Okapi Systems utilize information from inlet, outlet and ambient room temperature sensors to calculate when the fan should turn on, how fast the fan should run to optimize the heat-transfer to the passing air within the collector, and when the fan should turn off, without leaving any significant amount of heat (that is above the room temperature) left in the collector to be wasted.

This is a technological approach designed to optimize the heating effects within the space you are trying to heat. It truly maximizes your solar air heater's abilities. We are certain you will find that heat coming out near floor-level will definitely heat up your room better and faster.

Check out this video explaining more about thermo-conductivity and how to best heat a room:

Would you install a fan heater near the ceiling? Of course not!


I am building a Huge solar heater. How big a fan will Okapi run?

posted Jul 25, 2014, 4:28 PM by Greenhill EnviroTechnologies Inc.   [ updated Jul 26, 2014, 7:12 AM ]

When building a really big heater, it is tempting to want to use one really powerful fan. Before you consider such a large fan, with such high CFM, we would suggest for you to consider having two or up to 4 of our standard fans, operating a 3 inch diameter inlet/outlet pair, each. Essentially it is like dividing up your giant heater into a few smaller, more standard-sized heaters and using an Okapi 2.i or even a combination of Okapi Systems to operate numerous fans indpendently within your giant heater.

We highly recommend you consider this kind of set-up for your system, to keep the noise-level low (if that is of concern for you), your running costs low and for ease of set-up. 

A single fan operating a very large in area solar collector, no matter how powerful it might be, will not likely be able to move all that air evenly and effectively thoughout the collector. This could result in hot pockets of low air-flow where not heat gets harvested. 

You can keep you solar air collector box wide open, or partition it into 4ft wide x 8 or 10ft high areas for each inlet-outlet section: that is up to you, the designer.

It is ideal to have independent control of the air flow in each section or partition to control the temperature within the whole solar collector system better. A very large sized collector could potentially heat up more on one end in the early part of the day, and cool down faster on the other end later in the day. Also if there are any passing shadows, you will have better control of the air flow through the sections of the heater box that could be at drastically different temperature levels.


Once you have considered this set-up, and still feel you want to order a more powerful fan(s), our Okapi systems are made to operate more powerful fans than our standard fan.

Okapi can run a fan with these requirements:
          •  4 Amps (48watts) maximum
          •  12VDC 
          •  with PWM (Pulse Width Modulation: variable speed control)
Contact us if you wish to discuss the best fan system set-up for your solar air heater.

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